Sealed Enclosure for Transporting and Storing Semiconductor Substrates

ABSTRACT

The present invention relates to a sealed enclosure for transporting and storing semiconductor substrates, the enclosure comprising a sealed container and support means placed inside the container and including trays for supporting substrates. The container comprises two touching half-shells that can be spaced apart in order to open the container, and each end of said support means is secured mechanically to a respective one of said half-shells. The total height of said means varies depending on whether the container is opened or closed, the trays being separated from one another by equal distances. Said support means preferably comprise an alternation of segments and ball joints having end segments that are mechanically connected to respective ones of the half-shells. Under such circumstances, the total height of said support means varies by the alternation of segments and ball joints moving concertina-like.

The present invention relates to the field of substrate transport andstorage, in particular during the various steps of fabricatingmicroelectronic components, e.g. for making the components ofmicro-electrical mechanical systems (MEMS) or of opto-micro-electricalmechanical systems (MOEMS). The invention relates more particularly to asealed enclosure for transporting and storing such substrates, which aregenerally in the form of glass masks of polygonal shape or ofsemiconductor-material wafers of circular shape, such as silicon wafers.

Between the various fabrication steps, substrates are transported andstored in sealed enclosures containing a controlled atmosphere thatprotects them from the pollution present in the atmosphere of whiterooms. Usually, the enclosures contain one substrate (a silicon waferhaving a diameter of 200 millimeters (mm) or of 300 mm) or a pluralityof substrates in a stack. At present, the sealed enclosures commonlyused contain one to 25 substrates. Each substrate rests on an individualsupport and the substrates are separated from one another by a spacethat is minimized in order to obtain storage enclosures of smalldimensions.

Such sealed enclosures are coupled with inlet/outlet interfaces offabrication equipment with the help of an airlock and robotic means. Afirst robot transports the substrate from the transport sealed enclosureto a load chamber. The load chamber is put to low pressure. Thereafterthe robot of the transfer chamber transports the substrate from the loadchamber to a process chamber. The space available under the substrate,when placed in the load chamber or in the transport enclosure, must besufficient to allow the arm of the robot initially to pass under thesubstrate. Thereafter, the arm must be capable of rising sufficientlyfor the substrate to rest no longer on its support but instead on therobot's arm, which can then move the substrate towards the processchamber.

It will be understood that sealed enclosures capable of satisfying theabove-mentioned constraints are large in volume. Unfortunately, thespace available for storage in a white room is small because of the costof making and maintaining a white room. The quantity of enclosures, andthus of substrates, that can be stored therein is limited. It wouldtherefore be appropriate to reduce the size of such sealed enclosures.

Patent document US-2002/018 703 describes an installation comprising aprocess chamber connected to a transfer chamber communicating with loadchambers, each containing a cassette for temporary storage ofsemiconductor substrates. The load chambers are connected by substratetransport means to a shelf having storage compartments for receiving thesubstrates. A robot transfers the substrate from the storage compartmentto the cassette situated in the load chamber. A mechanism included inthe cassette comprises a plurality of trays and means for supporting thetrays and guiding their displacement. To insert and/or extract asubstrate into and/or from the cassette, the tray supporting thesubstrate is moved away from the other trays by support and guide meansthat move away the stacked trays on either side of the selected tray. Alocking device locks the tray in a position such that it is spaced apartfrom the adjacent trays situated above it and below it. The tray is thusaccessible for manipulation by the robot.

In addition, the sealed enclosure must enable a controlled atmosphere tobe conserved around the substrates in order to avoid them beingcontaminated during the transport and storage stages. Wafers can remainfor several weeks in the semiconductor fabrication unit between thevarious process steps. Throughout this time, the semiconductorsubstrates need to be protected against any risk of pollution comingfrom the white room, and also from the substrate itself. That is one ofthe reasons why provision is made to transport and store them in sealedenclosures under a controlled atmosphere.

An object of the present invention is to propose a sealed enclosurestructure for semiconductor substrate transport and storage whilenevertheless presenting space around the substrate enabling it to beinserted into and/or extracted from the enclosure by the robotic meanscommonly used in existing installations.

In addition, the enclosure of the invention must enable a controlledatmosphere to be conserved around the substrates in order to preventthem being contaminated during transport and storage stages, by ensuringsufficient sealing in a manner that is simple and inexpensive.

Finally, the transport enclosure must be capable of coupling with theloading/unloading interfaces of common fabrication equipment.

The present invention provides a sealed enclosure for transporting andstoring semiconductor substrates, the enclosure comprising a sealedcontainer and support means placed inside said container and includingtrays for supporting said substrates, the enclosure being characterizedin that said container comprises two touching half-shells that moveapart to open said container, and in that each end of said support meansis mechanically secured to a respective one of said half-shells.

Thus, the total height of the support means varies depending on whetherthe container is open or closed, the trays being spaced apart by equaldistances.

The sealed enclosure of the present invention has the advantage of beingcompact once closed, thereby facilitating storage and transport. Becauseof its small inside volume, controlling its atmosphere is simpler,particularly with respect to pollution. In addition, its weight and itsmanufacturing costs are reduced, and it requires an interface of smallsize with the installation.

In a particular embodiment, the support means include alternatingsegments and ball joints. More preferably, the alternation of segmentsand ball joints has a segment at each end, each of said end segmentsbeing mechanically connected to a respective one of said half-shells.

Advantageously, every other ball joint carries a tray on which a saidsubstrate rests. Under such circumstances, the total height of thesupport means preferably varies by a concertina movement of the isalternating segments and ball joints.

The half-shells making up the container are joined together via aflexible gasket. On retracting, the support means compress said flexiblegasket in order to seal said container.

In order to make the enclosure easier to manipulate, the containerincludes at least one handle and/or a locking device. The locking devicepreferably co-operates with the handle.

The present invention also provides a method of extracting a substratefrom an enclosure as described above. The low-pressure enclosure isplaced in a load chamber that is likewise at low pressure. The methodcomprises the following steps:

-   -   increasing the distance between the trays by moving the        half-shells apart;    -   introducing robotic means between two contiguous trays;    -   lifting the substrate placed above the robotic means;    -   extracting the robotic means together with the substrate; and    -   reducing the distance between the remaining trays by uniting the        half-shells.

The present invention also provides a method of inserting a substrate inan enclosure as described above. The low-pressure enclosure is placed ina load chamber at low pressure. The method comprises the followingsteps:

-   -   increasing the distance between the trays by moving the        half-shells apart;    -   inserting robotic means carrying the substrate between two        contiguous trays;    -   placing the substrate on the tray located beneath the robotic        means;    -   extracting the robotic means; and    -   reducing the distance between the trays by uniting the        half-shells.

Other characteristics and advantages of the present invention appearfrom the following description of embodiments given by way ofnon-limiting illustration and from the accompanying drawings, in which:

FIG. 1 is a fragmentary diagrammatic view in vertical section of thetransport and storage enclosure of the invention in the storageposition;

FIG. 2 is a fragmentary diagrammatic view in vertical section of theFIG. 1 enclosure while a substrate is being inserted or extracted;

FIGS. 3A, 3B, and 3C are fragmentary diagrammatic views in sectionshowing a substrate being extracted from an enclosure of the inventionfor transfer into a process chamber;

FIG. 4 shows a particular embodiment of the invention; and

FIG. 5 is a diagrammatic horizontal section view of the transport andstorage enclosure of the invention.

In an embodiment of the invention shown in FIG. 1, there can be seen anenclosure 1 of the invention in its closed position for storage. FIG. 2shows the same enclosure 1 in the open position during an operation ofextracting or inserting a substrate wafer, while the enclosure 1 isinside a load/unload chamber of a fabrication and processinginstallation. Identical references designate the same elements as inFIG. 1.

The enclosure 1 comprises a container 2 made up of a top half-shell 2 aand a bottom half-shell 2 b. The two half-shells 2 a and 2 b are incontact via a flexible gasket 3 which is compressed to seal theenclosure 1. The circularly arcuate shape of the half-shells 2 a and 2 benables them to withstand better the pressure of the outside atmosphere.The enclosure 1 is provided with a manipulation handle 4 made up of twoportions 4 a and 4 b connected respectively to the two half-shells 2 aand 2 b. The handle 4 is provided with a locking device 5 to prevent anyuntimely opening. The locking device 5 can be opened by a robot insidethe load chamber of the processing installation once it is evacuated.The enclosure 1 may advantageously be provided with legs 6 forstabilizing it on a plane surface and facilitating its alignment duringautomatic manipulations.

Inside the enclosure 1, there are support means 7 for supportingsubstrate wafers 8. The support means 7 for supporting the substratewafers 8 are flexible and capable of deploying when the enclosure 1 isopened, as shown in FIG. 2, so as to provide accessibility to thesubstrate wafers 8 for standard robotic means. When the enclosure 1 isclosed, the support means 7 fold so as to minimize their height.

The support means 7 comprise movable segments 7 a interconnected by balljoints 7 b, 7 c. The set of movable segments 7 a and of ball joints 7 b,7 c uniting them is fastened by fastener segments 7 d and 7 erespectively to the top half-shell 2 a and to the bottom half-shell 2 bof the enclosure 1. While the enclosure 1 is being closed, the set ofmovable segments 7 a and of ball joints 7 b, 7 c folds concertina-likeso that every other ball joint 7 b is offset towards the center of theenclosure 1, while the ball joints 7 c between them are offset outwards.The ball joints 7 b that move towards the center of the enclosure 1during closure carry trays 9. In the storage position, the enclosure 1is closed and the trays 9 are spaced apart by a distance ds. Once theenclosure 1 has been opened for loading and/or unloading substratewafers 8, the trays 9 are spaced apart at a distance dc that is muchgreater than ds.

A stud 10 is placed on each tray 9. The substrate wafers 8 rest on thestuds 10 and they are held laterally by stop pieces 11. The studs 10must present surfaces that are perfectly clean and free from pollutingparticles. A portion in relief 12 is placed under the tray 9 in registerwith the stud 10. The portions in relief 12 are flexible parts, e.g. ofthe spring type or else they are constituted by an elastic material suchas a silicone or an elastomer. When the enclosure 1 is closed in thestorage position, each portion in relief 12 bears resiliently againstthe substrate wafer 8 situated immediately beneath the tray 9 carryingthe portion in relief. The portions in relief 12 thus enable thesubstrate wafers 8 to be held in stationary position in order to preventany damage during displacement of the enclosure 1 and in order toprevent them deforming during storage periods. For the substrates 8 tobe held properly, at least three trays 9 are required.

FIGS. 3A to 3C show the successive steps in unloading a substrate wafer.The enclosure 1 in the closed position and containing an atmosphere atlow pressure is placed in the load/unload chamber 30 associated with thetransfer chamber 31 of a fabrication or process installation forsemiconductor substrates.

The load chamber 30 contains a mechanical compression system 32 enablingthe enclosure 1 to be opened and closed, and the transfer chamber 31contains a manipulator robot 33 enabling the substrate 8 to be graspedand displaced. The compression system 32 comprises an extensible arm 32a having an end carrying means 32 b for locking and/or unlocking thelocking device 5 placed in the handle 4 of the enclosure 1, andassociated means 32 c for opening the enclosure 1 by raising the tophalf-shell 2 a. The arms 32 a and the associated means 32 c are carriedby a common base 32 d fastened to the wall of the load chamber 30.

There follows an explanation of how a substrate 8 is inserted,transported, and extracted using the transport and storage enclosure 1of the present invention.

In order to load one or more substrates 8 into an empty enclosure 1, theenclosure 1 is opened at atmospheric pressure in the white room, andthen placed in the load/unload chamber 30 of the installation. The loadchamber 30 is closed and evacuated, thereby also evacuating the openenclosure 1. Once the enclosure 1 and the load chamber 30 have reached apressure that is sufficiently low, the transfer chamber 31, which isalso at low pressure, opens. The manipulator robot 33 has enough room tomove one or more substrates into the enclosure. Once the substrate(s) 8is/are placed inside the enclosure 1, a mechanical compressor system 32of the actuator or spring type bears down on the transport enclosure 1,thereby:

-   -   compressing the flexible support means 7 for supporting        substrates 8 that are placed inside the enclosure 1 so that the        two half-shells 2 a and 2 b come into contact with each other,        meeting in sealed manner by virtue of the gasket 3, and being        held together by means of the locking device 5; and    -   holding the substrates 8 inside the enclosure 1 by a mechanical        positioning and holding system comprising the portions in relief        12 and the studs 10 associated with the centering and holding        pieces 11.

The size of the enclosure 1 is minimized by the applied compression,thereby making it easy to transport to a storage location or to anyother compatible equipment. The number of enclosures that can be storedin a given volume is thus substantially increased compared with theprior art.

Finally, with the enclosure 1 being held in compression by themechanical compression system 32, the load chamber 30 is progressivelyreturned to atmospheric pressure, thereby having the effect of keepingthe enclosure 1 in the closed position because of the pressuredifference between atmospheric pressure in the load chamber 30 and thelow pressure inside the enclosure 1. The mechanical compression system32 can then be deactivated since its effect is naturally compensated bythe pressure difference. Nevertheless, in order to provide securityagainst possible leaks, the mechanical compression system 32 can remainactivated while the load chamber 30 is being opened, thus enabling theloaded enclosure 1 to be retrieved with low internal pressure. Thesealing of the enclosure 1 is then maintained naturally by the pressuredifference between the inside of the enclosure 1 which is at lowpressure and the outside environment in the white room which is atatmospheric pressure. Two levels of security are put into place to avoidany leaks: firstly the locking device 5 enables the gasket 3 to be keptunder compression as are the flexible support means 7 inside theenclosure 1, and secondly the stress exerted by the external atmosphericpressure in the white room which applies light mechanical compressionall around the enclosure 1.

In order to unload one or more substrates 8, the closed enclosure 1,while maintained at low pressure and in compression by the lockingdevice 5, is inserted into the load chamber 30 which is at theatmospheric pressure of the white room, as shown in FIG. 3A. The loadchamber 30 is then evacuated progressively. The enclosure 1 will expandlittle by little. So long as the pressure inside the chamber 30 isgreater than the pressure inside the enclosure 1, pressure exerts aforce on the container 2 that opposes opening of the enclosure 1. Thehandle 4 is unlocked once the pressure inside the load chamber 30 isequal to the pressure inside the enclosure 1. The height to which theenclosure 1 opens is limited by the above-described compression system32 acting as a high abutment (FIG. 3B).

Once the enclosure 1 is in the open position, the manipulator robot 33can come and find the substrates 8 that have become accessible. An armof the manipulator robot 33 is inserted, as shown by arrow 34 in FIG.3A, between two trays which are spaced apart sufficiently for this to bepossible. The arm lifts the substrate that is placed above it as shownby arrow 35 in FIG. 3B. The manipulator robot 38 carrying the substratethen withdraws along arrow 36 shown in FIG. 3C.

In a particular embodiment shown in FIG. 4, the enclosure 1 is fittedwith a pressure sensor 40 that measures the pressure inside theenclosure 1. The measurement is transmitted by a signal at radiofrequency (RF). It serves to determine the exact moment the enclosure 1opens and it can also serve to provide continuous monitoring of theenvironment inside the enclosure 1. The signal receiver may bepositioned either inside the chamber 30 or outside the installation. Ina variant, the system may also be fitted with temperature sensors,humidity sensors, and/or with sensors for measuring some other propertyof gas.

FIG. 5 is a horizontal section view of the enclosure 1 seen from above.The support means 7 are placed in a triangle configuration around thesubstrate 8 so as to hold it in place while the enclosure 1 is beingmanipulated. The arm of the manipulator robot 33 is placed on the sideof the container 2 of the enclosure 1 that is remote from its handle 4provided with the locking device 5. Once compressed, the gasket 3projects into the inside of the enclosure 1 and contributes to holdingthe substrate 8.

1. A sealed enclosure for transporting and storing semiconductorsubstrates, the enclosure comprising a sealed container and supportmeans placed inside said container and including trays for supportingsaid substrates, the enclosure being characterized in that saidcontainer comprises two touching half-shells that move apart to opensaid container, and in that each end of said support means ismechanically secured to a respective one of said half-shells.
 2. Anenclosure according to claim 1, in which the total height of saidsupport means varies depending on whether said container is open orclosed, said trays being spaced apart at equal distances.
 3. Anenclosure according to claim 1, in which said support means includealternating segments and ball joints.
 4. An enclosure according to claim3, in which said alternation of segments and ball joints has a segmentat each end, each of said end segments being mechanically connected to arespective one of said half-shells.
 5. An enclosure according to claim3, in which the total height of said support means varies by thealternating segments and ball joints moving concertina-like.
 6. Anenclosure according to claim 3, in which every other ball joint carriesa tray on which a said substrate rests.
 7. An enclosure according toclaim 1, in which said half-shells are united via a flexible gasket. 8.An enclosure according to claim 7, in which said support means compresssaid flexible gasket to seal said container.
 9. An enclosure accordingto claim 1, in which said container includes at least one handle.
 10. Anenclosure according to claim 1, in which said container includes alocking device.
 11. An enclosure according to claim 10, in which saidcontainer includes at least one handle and said locking deviceco-operates with said handle.
 12. A method of extracting a substratefrom a low-pressure enclosure placed in a low-pressure load chamber,said enclosure comprising a sealed container and support means placedinside said container and including trays for supporting saidsubstrates, said container comprising two touching half-shells that moveapart to open said container, each end of said support means beingmechanically secured to a respective one of said half-shells, the methodbeing characterized in that it comprises the following steps: increasingthe distance between the trays by moving the half-shells apart;introducing robotic means between two contiguous trays; lifting thesubstrate placed above the robotic means; extracting the robotic meanstogether with the substrate; and reducing the distance between theremaining trays by uniting the half-shells.
 13. A method of inserting asubstrate in a low-pressure enclosure placed in a low-pressure loadchamber, said enclosure comprising a sealed container and support meansplaced inside said container and including trays for supporting saidsubstrates, said container comprising two touching half-shells that moveapart to open said container, each end of said support means beingmechanically secured to a respective one of said half-shells, the methodbeing characterized in that it comprises the following steps: increasingthe distance between the trays by moving the half-shells apart;inserting robotic means carrying the substrate between two contiguoustrays; placing the substrate on the tray located beneath the roboticmeans; extracting the robotic means; and reducing the distance betweenthe trays by uniting the half-shells.